The present invention relates to a printed wiring board having bumps, ball pads or the like to which solder balls are applied, and a method of manufacturing the same.
There is a conventional printed wiring board which has a conductor circuit on an insulating substrate and a surface insulating layer provided on the surfaces of the insulating substrate and the conductor circuit and formed of a solder resist layer or a glass cloth resin layer.
In general, bumps or ball pads are provided on the surface of the printed wiring board which is connected to an electronic part, another printed wiring board or the like via solder balls applied on those bumps or ball pads.
The bumps or ball pads are formed by exposing the conductor circuit underlying the surface insulating layer by local removal of the surface insulating layer.
This conventional printed wiring board has the following drawbacks.
At the time of forming bumps or ball pads on the printed wiring board, the surface insulating layer is locally removed, thereby exposing the sides of the conductor circuit. This may reduce the strength of adhesion between the conductor circuit and the insulating substrate.
In providing solder balls on the bumps or ball pads with the above structure, the solder balls on the bumps or ball pads may be flattened due to the exposed sides of the conductor circuit and high adhesion strength of the solder balls to those sides.
When the solder balls are flattened, it is not possible to maintain the proper distance between the insulating substrate and an electronic part, another printed wiring board or the like which is connected to this printed wiring board via the solder balls. This may result in a reduced reliability of connection between them.
As the amount of heat generated by electronic parts tends to increase, printed wiring boards are provided with heat discharging means such as connection of solder balls or formation of thermal via holes for discharging heat. The heat discharging performance of the conventional printed wiring boards, however, has not yet been improved to a satisfactory level.
Accordingly, it is an object of the present invention to provide a printed wiring board with excellent heat discharging performance, which has an enhanced adhesion strength between a conductor circuit and an insulating substrate and ensures a high reliability of connection between this printed wiring board and a mounted part, such as another electronic part or another printed wiring board at the time of connecting such a part to this printed wiring board via solder balls applied to bumps, ball pads or the like provided on the conductor circuit and the insulating substrate, and a method of manufacturing the same.